Reclaimed elastomer materials, or “micronized rubber powders” (“MRP”), which include reclaimed vulcanized elastomer particles, are used in a variety of applications, including elastomeric compositions (e.g., tire tread compounds for vehicle tires), plastics compositions (e.g., as fillers for polyolefins), asphalt fillers, and others. In many of these applications, the reclaimed elastomer particles are used as “filler” in place of a portion of the virgin polymer material. One of the primary reasons for the use of vulcanized elastomer particles is cost. Namely, the vulcanized elastomer particles typically are significantly less expensive than virgin (i.e., non-reclaimed) rubber or plastic, and can be used as a “filler” in elastomer or plastic compositions to reduce the overall manufacturing cost of the composition. Further, because vulcanized elastomer particles are typically made from recycled or reclaimed material (e.g., vulcanized scrap from manufacturing processes and used tires or other elastomeric products), reincorporating vulcanized elastomer particles into elastomer and plastic compositions reduces landfill waste and results in a more environmentally-friendly product.
Generally, the vulcanized elastomer particles or MRP used in such reclaimed elastomer materials are small in size (e.g., 2 mm or less in diameter) and are produced in a variety of ways, including by cryogenic grinding, chemical processes, and other methods. As set forth above, the reclaimed elastomer material used to manufacture the particles is typically obtained from previously-manufactured products (e.g., unused or used vehicle tires) or from vulcanized scrap generated during a manufacturing process (e.g., vulcanized scrap generated from the tire manufacturing process).
Conventionally, the compositions of these reclaimed elastomer materials conform to the American Society for Testing and Materials (ASTM) standards (and, specifically, to ASTM D-5603-01 for rubber compounding materials), which classifies materials according to the maximum size of the particles comprising the composition. Generally, particle sizes are classified according to U.S. Standard Mesh sizes (or simply, “mesh”). For example, an 80 mesh particle comprises a diameter of approximately 177 μm, a 140 mesh particle comprises a diameter of approximately 105 μm, a 325 mesh particle comprises a diameter of approximately 44 μm, and so on. U.S. Standard Mesh sizes are readily available from many public sources and are known to those of ordinary skill in the art.
Heretofore, the size of vulcanized elastomer particles in a given classification of reclaimed elastomer material (i.e., micronized rubber powder) tended to centralize around the maximum particle size in the formulation, with little distribution or variation in the size of particles in the particular classification (i.e., the particle size distribution was relatively uniform). Previously, it was assumed that reclaimed elastomer material compositions having a wide range of particle sizes would exhibit poor performance characteristics and would, therefore, be relatively undesirable for many applications. However, producing reclaimed elastomer material compositions with uniform particle size distributions via certain milling processes, such as cryogenic turbo mill processes, can be costly as careful screening, sorting, and distribution of the vulcanized particles is typically necessary.
Further, reclaimed vulcanized elastomer particles are relatively inert and therefore non-reactive with virgin elastomer matrix materials. Therefore, reclaimed elastomer material compositions comprising reclaimed vulcanized elastomer particles are of limited use as filler in rubber or plastic compositions as high levels of the reclaimed vulcanized elastomer particles generally lower the overall physical properties of rubber and plastic compositions. This limitation can be eased by the use of devulcanized elastomer particles, i.e., particles that have undergone a devulcanization treatment or other treatment method (e.g., thermal, mechanical, or chemical) that results in a chemical modification to the surface of the cured elastomer particles. Such chemical modifications to the surface of the reclaimed elastomer particles leads to improved interaction between the reclaimed particles and the virgin elastomer matrix materials. Due to the additional processing involved, however, devulcanized or otherwise chemically modified elastomer particles tend to be more expensive than reclaimed vulcanized elastomer particles.
Therefore, there is a long-felt but unresolved need for elastomeric compositions that comprise reclaimed elastomer material but are less expensive to produce than conventional elastomeric compositions while also retaining mechanical properties comparable to elastomeric compositions containing no reclaimed material.